This invention relates to a process for the removal of calcium from calcium-containing petroleum crudes, heavy hydrocarbonaceous residua or solvent deasphalted oils derived from crude and residua, using hydroxocarboxylic acids, particularly citric acid, as sequestering or chelating agents. A few, but increasingly important, petroleum crude feedstocks and residua contain levels of calcium which render them difficult, if not impossible, to process using conventional refining techniques. Specifically, the calcium contaminant causing particular problems is in the form of non-porphyrin, organometallically-bound compounds. These species have been only recently discovered in crude oils, very heavy crude oils in particular, and are apparenty relatively rare. One class of these calcium-containing compounds identified, in particular, is the calcium naphthenates and their homologous series. These organo-calcium compounds are not separated from the feedstock by normal desalting processes, and in a conventional refining technique they can cause the very rapid deactivation of hydroprocessing catalysts. Examples of feedstocks demonstrating objectionably high levels of calcium compounds are those from the San Joaquin Valley in California. Generally, these crudes are contained in a pipeline mixture referred to an San Joaquin Valley crude or residuum.
The problems presented by calcium in petroleum feedstocks and their necessity for removal have only been recently appreciated, and the prior art contains few references specifically to its removal. Metals removal generally using organic compounds, however, has been addressed in the prior art, specifically for the removal of known metallic contaminants, such as nickel, vanadium, and/or copper. These compounds are also ordinarily found in feedstocks as porphyrins, and other organometallic compounds.
In U.S. Pat. No. 3,052,627, Lerner, metals-contaminants are removed from crude petroleum feedstocks using a 2-pyrrolidone-alcohol mixture. In U.S. Pat. No. 3,167,500, Payne, metallic contaminants, such as metal-containing porphyrins, are removed from petroleum oils using a condensed polynuclear aromatic compound having a preferred C/H ratio and a molecular weight, ordinarily called pitch binders. In U.S. Pat. No. 3,153,623, Eldib et al., selected commercially available organic compounds of high dielectric strength were added to assist in the electrically directed precipitation removing metals with the polar organic molecules.
It has now been unexpectedly found that the calcium-containing contaminants may be effectively removed from hydrocarbonaceous feedstocks by binding the calcium compounds using citric acid and its salts.